The advantages, conveniences and comforts that have been achieved by the use of satellites have become expected or even required nowadays. The use of satellites and especially telecommunications satellites is essentially required for carrying out many different functions and operations. For example, data and information are acquired, transmitted, and relayed by satellites in the fields of weather forecasting based on earth studies and weather pattern recognition, environmental studies and monitoring, reconnaissance, telephone communications, and television transmissions, among others. Additionally, it has now become possible to achieve a worldwide telephone network using mobile telephones linked through satellite communication. All of these manmade celestial bodies require a continuous supply of electrical power, and in some cases at a rather substantial power level, in order to carry out their required functions of acquiring, transmitting, and relaying data and other information. The necessary power supply must operate reliably without problems and without interruptions over a long operating lifespan. In order to provide the necessary electrical energy, it has been typical to use solar generators comprising solar cells mounted on suitable carrier structures such as panel structures. In this context, the carrier structure is suitable if it is able to reliably withstand the arising loads, is compatible with the material of the solar cells, and still remains lightweight and cost economical. The arising loads include the mechanical loads during launch and during deployment, for example, while the compatibility between the support structure and the solar cell material includes compatibility of the respective thermal expansion coefficients of the materials and electrical insulation or isolation of the solar cells, for example.
More specifically, solar generators suitable for powering satellites must be able to reliably provide a substantially constant power output during a prescribed operating lifetime on the order of 10 to 12 years. Solar cells made of silicon or gallium arsenide on a lightweight support structure are particularly suitable in this context. The support structure in turn must comprise certain characteristics so as not to negatively influence other components of the satellite, such as antennas, tanks, orbital path tracking systems and the like.
The major mechanical loads on the solar generator arise during the launch process, and especially involve vibrations with an acceleration of 30 Gs, i.e. 30 times the earth's gravity. In order to withstand these mechanical loads, the solar generator, and particularly the support structure, must be so designed and constructed to withstand the forces arising from such vibrations and such extreme acceleration conditions. An additional mechanical load results from the noise pressure that arises under the aerodynamic fairing or nose cone at the nose of the rocket or launch vehicle due to the extremely loud noise generated by the rocket engines upon ignition and during the launch phase. The portions of lightweight support structures that are most seriously endangered by this noise pressure loading are sandwich composite components having extremely thin cover skins.
A few minutes after a successful launch of a satellite, the various functions of the satellite are tested and monitored while the satellite is located in a low earth orbit. Then, the solar generator panels are unfolded and deployed, before the telecommunications satellite is moved through a transitional orbital path to its final geostationary orbital path by means of reignition of the rocket engine or positional thrusters. The solar generator typically includes two solar panels or wings having a length of up to 12 m. These long solar panel wings present an inertial mass such that the corresponding support structure is subject to a bending load upon the ignition and again upon the shut-down of the satellite engine or thrusters. Once the satellite is in a stable orbit, then the solar panel support structures are only subject to loads caused by temperature variations and associated thermal expansion of the components.
Since it is an especially important goal to achieve a low weight of the solar generator in flying bodies such as earth-launched satellites, it is desirable to use fiber-reinforced composite materials for fabricating the support structures, because such composite materials provide a considerably higher specific strength and stiffness in comparison to all metal materials. In order to achieve the stiffest and lightest support structure possible, it is especially suitable to use laminates of high modulus fibers in the form of a sandwich construction. The basic arrangement of a sandwich construction, which may be used as a support structure for the solar cells of a solar generator for a telecommunications satellite, is shown in FIG. 1. FIGS. 2 and 3 show conventional improved support structures that are able to withstand greater mechanical loads than the simpler structure shown in FIG. 1.
It has been determined that the main mechanical loads effective on the support structure comprise vibrations in the frequency range from 30 Hz to 100 Hz, while secondary loads resulting from the noise pressure arise in a frequency range from 150 Hz to 500 Hz. The loads resulting from the noise pressure during launch of the rocket increase sharply with the dimensions of the solar generator, and especially the panel area dimensions thereof. Thus, the maximum size of the solar generator is limited by its ability to withstand the noise pressure loads resulting during launch. Moreover, the deformations of the support structure resulting from the vibrations and noise pressure cause damage to the sensitive solar cells mounted on the support structure.